Ovarian follicular development is a significant and complex process which involves the activation and growth of the oocyte as well as the growth and differentiation of ovarian follicle cells. Although there have been numerous studies on the structure and function of the cell types associated with ovarian follicles, the vast majority of these studies have concentrated on the late stages (late preantral to antral) of follicular development. To date, few studies have been carried out to study the factors which regulate the early stages of follicular cell differentiation and function. It is therefore proposed to carry out more detailed studies to determine which factors, including hormonal and extracellular matrices are important in regulating the early events of ovarian follicular cell differentiation. These studies are designed to: (1) utilize immunocytochemical localization methods to determine the appearance of extracellular matrix components during early stages of folliculogenesis in relation to the development and differentiation of follicular cells; (2) determine the roles of purified matrix components, complex extracellular biomatricies (including the zona pellucida), and hormones on the differentiation of cultured follicular cells of primary and secondary follicles using serum-free cell culture systems; and (3) develop antibodies to specific ovarian follicular proteins (including those of the zona pellucida) which are isolated from cell culture systems to use in studies as markers to study early follicular development. These studies should allow us to develop a better understanding of the basic mechanisms which regulate these early stages of cell differentiation of the follicular cells.